HD and digital channels come in two flavors, Unencrypted and encrypted. If you have a QAM tuner, you can get all the digital and HD channels that are unecrypted, and you need the cable card for the encrypted (premium) ones. Most cable providers dont encrypt the local channels in HD, so you can get them with QAM.
With my qam tuner I get HD PBS, NBC, ABC, WB, FOX, HBO, CBS, and a few others I rarely watch. How HBO got in there I have no idea, but the cable guy said not to worry about it, I'm not doing anything illegal and just be happy it comes in.
Unfortunately, I cant get discovery HD as it is encrypted, but its a small price to pay for all the other channels.
Digital wise, I hardly look through them all, but I would say I have about 50 music channels, and 30 or so regular channels, cant tell you what they are off the top of my head though.
So, its worth a shot when you get your new set. Plug in the cable that goes to your modem and do a channel search. Go through each channel individually, my HD channels show up as strange numbers between 118 and 130. For example, some of my channels are 125.14 or something like that.